For reliable determination of the presence and/or quantity of a particular analyte, proper calibration of the analytical instrument is required. Most typical vapor-phase calibration sources that can provide a known quantity of a particular analyte vapor at an accuracy in the high part-per-trillion (ppt) range (typically on the order of 100 nanograms or so) are too complex and too large to be conveniently used in the field to calibrate remote sensors or portable analytical instruments such as small gas chromatographs, mass spectrometers, and ion mobility spectrometers. There is a need for a small, simple-to-use calibration source that can be readily employed when field-portable instruments or unattended field sensors need recalibration to ensure reliable measurements since field conditions or instrument characteristics may change.